So-called air-spun yarns are known, which are produced wherein a fibrous sliver is drawn in a high-speed drafting system and fed to a spinning system using an air nozzle. In this process, specially constructed air nozzles engage with a portion of the external fibers of the sliver and wrap same spirally around the fiber strand. As a result the fiber strand receives very little strength, which nonetheless suffices to wind the drawn and slightly strengthened roving downstream of the nozzle head, for example, into a cross-wound package. Such air-spun yarns also form the basis for plied yarns, which are available on the market, for example, under the brand name "Plyfil". "Plyfil" is a trademark of Spindlefabrik Suessen Schurr, Stahlecker & Grill GmbH of Germany and relates to a system of forming yarns. The "Plyfil" system proceeds from combining two of such drawn and slightly strengthened rovings from two adjacent spinning pots, i.e., two individual strands are plied and both strands are jointly wound into a cross-wound package for example. Subsequently, this package is creeled in a twisting machine, for example a spindle assembly of two-for-one twisting machine, to twist the two strands about their common axis, so that a true twist forms, which has not only a common twist of both strands, but also a twist in the two individual strands.
Only as a result of such a twisting does a yarn form, which possesses an adequate strength for the subsequent processing steps and the desired properties necessary therefor.
For the strengthening and/or twisting of feed yarns having only a relatively small strength, which is understood within the scope of the present invention to include, for example, air-spun yarns as well as ply yarns, the use of a spindle assembly of a yarn twisting machine having a rotating pot mechanism could be considered. However, a precondition for strengthening and/or twisting the yarn with such a spindle assembly is that the feed yarn including a plied yarn has received a slight twist already in a preparatory processing step. For the purpose of strengthening and/or twisting such a feed yarn, which possesses already a slight preliminary twist, the feed yarn package is inserted into the pot mechanism of the twisting spindle assembly, which is then rotated, so that the feed yarn is withdrawn from the package, in most cases a double-flanged spool, while forming a balloon, and advanced to the yarn guide eyelet in the apex of the yarn balloon. As the spindle rotates, the pot surrounding the package rotates likewise, with the yarn balloon contacting the pot.
It is possible to keep the two strands of a ply yarn together, even after applying further methods, for example, by entangling or bonding segments thereof, possibly also by the application of a heat treatment depending on the quality and character of the feed yarn being processed.
When, subsequent to the spinning process, a package or an assembly wound package is present without an adequate preliminary twist of the individual yarn strand or of the two or more wound strands of yarn, it will be impossible to process such a yarn in a spindle assembly of a twisting machine having a rotary pot mechanism. The problem lies in the lacking strength in such a feed yarn. The yarn layers of the package separate from the package surface as a result of the centrifugal force which occurs during the rotation of the pot twisting spindle, and swing about the wound yarn package in a manner comparable to the rings of Saturn. Thus, it will not be possible to carry out a stable yarn strengthening and/or twisting process.